Printer having head gap adjusting device

Abstract

A printer having a device for advancing and retracting a print head toward and away from a paper supporting platen, an automatic head gap adjusting device for controlling the head advancing and retracting device, to advance the print head until the print head comes into contact with a recording paper, and then retracting the print head by a predetermined distance, to thereby adjust a head gap between the paper and the print head, and an operator-controlled head gap adjusting device for manually operating said head advancing and retracting device, to thereby adjust the head gap. A mode selector is provided for selecting one of an automatic adjusting mode in which the head gap is adjusted by the automatic head gap adjusting device, and a manual adjusting mode in which the head gap is adjusted by the operator-controlled head gap adjusting device.

What is claimed is: 
     
       1. A printing apparatus comprising: a platen for supporting a recording medium;   a print head disposed movably in a transverse direction toward and away from said platen;   a head advancing and retracting device for moving said print head in said transverse direction;   automatic head gap adjusting means for controlling said head advancing and retracting device to advance said print head until the print head comes into contact with said recording medium and then retracting the print head by a predetermined distance, to thereby adjust a head gap between said recording medium and said print head;   operator-controlled head gap adjusting means for manually operating said head advancing and retracting device, to thereby adjust said head gap; and   adjusting mode selecting means for selecting one of an automatic adjusting mode in which said head gap is adjusted by said automatic head gap adjusting means, and a manual adjusting mode in which said head gap is adjusted by said operator-controlled head gap adjusting means.   
     
     
       2. A printing apparatus according to claim 1, wherein said operator-controlled head gap adjusting means is mechanically connected to said head advancing and retracting means, and comprises an operating lever which is manually operated to operate said head advancing and retracting means. 
     
     
       3. A printing apparatus according to claim 1, wherein said operator-controlled head gap adjusting means comprises operator-controlled switching means, and signal processing means connected to said switching means and said automatic head gap adjusting means and responsive to a signal generated by said switching means, for controlling said head advancing and retracting device. 
     
     
       4. A printing apparatus according to claim 1, further comprising position indicator means for indicating a position of said print head in said transverse direction. 
     
     
       5. A printing apparatus according to claim 4, wherein said position indicator means comprises a scale plate having graduations representative of the position of said print head, and a pointer movable relative to said scale plate in response to a movement of said print head in said transverse direction, to thereby cooperate with said graduations to indicate the position of the print head. 
     
     
       6. A printing apparatus according to claim 5, wherein said head advancing and retracting device comprises a stepping motor as a drive source, and an interval of said graduations of said scale plate is equal to a distance of movement of said pointer corresponding to an angle of rotation of said stepping motor which is obtained by one excitation cycle of the motor, said printing apparatus further comprising: phase memory means for storing data representative of an excitation phase of said stepping motor when said pointer is aligned with one of said graduation of said scale plate; and   hold-voltage applying means for applying a hold voltage to said stepping motor so as to establish said excitation phase stored in said phase memory means, when said manual adjusting mode is selected by said mode selecting means.   
     
     
       7. A printing apparatus according to claim 6, further comprising a positioning device for adjusting a position of said scale plate such that pointer points one of said graduations when said hold voltage is applied to said stepping motor, in said excitation phase stored in said phase memory means. 
     
     
       8. A printing apparatus according to claim 1, wherein said head advancing and retracting device comprises a drive source, a power transmission mechanism for transmitting a drive force of said drive source to said print head to move the print head in said transverse direction, and a clutch mechanism having a connecting state for transmitting said drive force of said drive source smaller than a preset value in a forward direction to advance the print head toward said platen, and a disconnecting state for inhibiting the transmission of said drive force exceeding said preset value to said print head, and wherein said automatic head gap adjusting means comprises clutch release detecting means for detecting said disconnecting state of said clutch mechanism, and stopping means for stopping an operation of said drive source that produces the drive force in said forward direction, when said disconnecting state of said clutch mechanism is detected by said clutch release detecting means.   
     
     
       9. A printing apparatus according to claim 8, wherein said clutch mechanism comprises: a drive member operatively connected to said drive source;   a driven member operatively connected to said print head;   a first and a second engaging portion which are provided on said drive and driven members, respectively, and which engage each other such that a movement to retract said print head is transmitted from said drive member to said driven member while a movement to advance the print head is inhibited from being transmitted from the drive member to the driven member; and   an elastic member having a predetermined pre-load biasing said first and second engaging portions of said drive and driven members for engagement of said first and second engaging portions with each other, said pre-load being smaller than said drive force of said drive source.   
     
     
       10. A printing apparatus comprising: a platen for supporting a recording medium;   a print head disposed movably in a transverse direction toward and away from said platen;   a head advancing and retracting device for moving said print head in said transverse direction;   automatic head gap adjusting means for controlling said head advancing and retracting device to advance said print head until the print head comes into contact with said recording medium and then retracting the print head by a predetermined distance to adjust a head gap between said recording medium and said print head;   said head advancing and retracting device comprising a drive source, a power transmission mechanism for transmitting a drive force of said drive source to said print head to move the print head in said transverse direction, and a clutch mechanism having a connecting state for transmitting said drive force of said drive source smaller than a preset value in a forward direction to advance the print head toward said platen, and a disconnecting state for inhibiting the transmission of said drive force exceeding said preset value to said print head; and   said automatic head gap adjusting means comprising clutch release detecting means for detecting said disconnecting state of said clutch mechanism, and stopping means for stopping an operation of said drive source that produces the drive force in said forward direction, when said disconnecting state of said clutch mechanism is detected by said clutch release detecting means.   
     
     
       11. A printing apparatus according to claim 10, wherein said clutch release detecting means comprises: head stop detecting means for detecting that said print head is stopped in said transverse direction;   drive detecting means for detecting that said drive source is in operation; and   clutch release determining means for determining that said clutch mechanism is placed in said disconnecting state, if said head stop detecting means detects that said print head is stopped, while said drive detecting means is detecting an operation of said drive source.   
     
     
       12. A printing apparatus according to claim 11, wherein said head stop detecting means comprises: a sensor for generating an operation signal indicative of an operation of a sensed member of said power transmission mechanism which is disposed between said clutch mechanism and said print head; and   stop determining means for generating said stop signal when said operation signal is absent.   
     
     
       13. A printing apparatus according to claim 12, wherein said drive source comprises a stepping motor, and said sensor comprises an encoder which produces a pulse signal in response to the operation of said sensed member of the power transmission mechanism, and wherein said drive detecting means comprises a motor detecting means for detecting each stepping operation of said stepping motor; and said clutch release determining means determines said disconnecting state when said motor detecting means has detected a predetermined number of stepping operations of said stepping motor while said pulse signals of said encoder are absent.   
     
     
       14. A printing apparatus according to claim 11, wherein said drive source comprises a stepping motor, and said drive detecting means comprises motor detecting means for detecting each stepping operation of said stepping motor. 
     
     
       15. A printing apparatus according to claim 11, wherein said head stop detecting means comprises: an encoder for generating a basic pulse signal and a direction pulse signal having a relative phase difference, in response to an operation of a sensed member of said power transmission mechanism which is disposed between said clutch mechanism and said print head; and   stop determining means for determining that said print head is moving in said transverse direction, only in a case where a level of said direction pulse signal upon one of successive rising and falling of said basic pulse signal is different from that of said direction pulse signal upon the other of said successive rising and falling of said basic pulse signal, said stop determining means determining that said print head is stopped in the other case.   
     
     
       16. A printing apparatus according to claim 15, wherein said drive source comprises a stepping motor, and said head stop detecting means comprises initial control means for activating said stop determining means after said stepping motor is operated a predetermined number of steps. 
     
     
       17. A printing apparatus according to claim 11, wherein said drive source comprises a stepping motor, and further comprising: an encoder for generating a basic pulse signal and a direction pulse signal having a relative phase difference, in response to an operation of a sensed member of said power transmission mechanism which is disposed between said clutch mechanism and said print head; and   out-of-synchronization determining means for determining that said stepping motor is placed in an out-of-synchronization state, if levels of said direction pulse signal upon rising and falling of said basic pulse signal are different from nominal levels which are determined by a direction in which said stepping motor is stepped.   
     
     
       18. A printing apparatus according to claim 12, wherein said sensor comprises an encoder which includes: a movable slit member moved with said sensed member and including a slit portion having a multiplicity of slits equally spaced apart from each other, and a non-slit portion extending from one end of said slit portion;   a stationary basic slit member and a stationary direction slit member which are fixedly disposed adjacent to said movable slit member and have respective slits which have different positional phases relative to said slits of said slit portion of said movable slit member;   a first light-emitting element and a first light-receiving element which are disposed in facing relation with each other such that said movable slit member and said stationary basic slit member are positioned between said first light-emitting and light-receiving elements, said first light-receiving element generating a basic pulse signal; and   a second light-emitting element and a second light-receiving element which are disposed in facing relation with each other such that said movable slit member and said stationary direction slit member are positioned between said second light-emitting and light-receiving elements, said second light-receiving element generating a direction pulse signal,   said encoder having a reference position which is established based on a boundary position of said movable slit member in which a boundary between said slit portion and said non-slit portion of said movable slit member is aligned with said stationary basic slit member.   
     
     
       19. A printing apparatus according to claim 18, wherein said drive source comprises a stepping motor, and further comprising reference setting means for establishing said reference position of said encoder, such that said reference position is spaced from said boundary position by an amount corresponding to a predetermined number of stepping operations of said stepping motor, in a direction from said non-slit portion of said movable slit member toward said slit portion. 
     
     
       20. A printing apparatus according to claim 12, wherein said drive source comprises a stepping motor, and said sensor comprises an encoder which generates pulse signals in response to an operation of said sensed member of said power transmission mechanism, said printing apparatus further comprising: reversing means for reversing a direction of operation of said stepping motor if no pulse signals are generated by said encoder during a predetermined number of stepping operations of said stepping motor in a reverse direction for retracting said print head away from said platen.   
     
     
       21. A printing apparatus according to claim 12, wherein said drive source comprises a stepping motor, and said sensor comprises an encoder which generates pulse signals in response to an operation of said sensed member of said power transmission mechanism, said printing apparatus further comprising: alarm means for generating an error signal indicative of an abnormality of the apparatus, if no pulse signals are generated by said encoder while said stepping motor is stepped in a forward direction for advancing said print head toward said platen.   
     
     
       22. A printing apparatus according to claim 12, wherein said drive source comprises a stepping motor, said printing apparatus further comprising memory means for storing data representing an abutting position of said print head in which the print head abuts on said platen in the form of the number of stepping operations of said stepping motor in a forward direction for advancing the print head from an initial position corresponding to a predetermined reference position of said sensor, until said clutch release detecting means detects said disconnecting state of said clutch mechanism. 
     
     
       23. A printing apparatus according to claim 22, further comprising medium thickness determining means for calculating a thickness of said recording medium, by subtracting a content of said memory means when the recording medium is placed on said platen, from a content of said memory means when said recording medium is not placed on said platen. 
     
     
       24. A printing apparatus according to claim 23, further comprising means for changing said predetermined distance by which said print head is retracted by said head advancing and retracting device under the control of said automatic head gap adjusting means, depending upon the thickness of said recording medium calculated by said medium thickness determined means. 
     
     
       25. A printing apparatus according to claim 10, wherein said clutch mechanism comprises: a drive member and a driven member;   a first and a second engaging portion which are provided on one and the other of said drive and driven members, respectively, and which engage each other such that a movement to retract said print head is transmitted from said drive member to said driven member while a movement to advance the print head is inhibited from being transmitted from the drive member to the driven member; and   an electric member having a predetermined pre-load biasing said first and second engaging portions of said drive and driven members for engagement of said first and second engaging portions with each other, said pre-load being smaller than said drive force of said drive member.   
     
     
       26. A printing apparatus according to claim 25, wherein said drive and driven members are rotating members, and one of said first and second engaging portions consists of a pin which is secured to said one of said drive and driven members so as to extend parallel to axes of rotation said drive and driven members, while the other of said first and second engaging portions consists of a recess which is formed in said other of said drive and driven members so that said pin engages said recess with a play in a rotating direction of said other of the drive and driven members, said elastic member (44) biasing said pin against one of opposite ends of said recess in said rotating direction. 
     
     
       27. A printing apparatus according to claim 10, wherein said power transmission mechanism comprises an eccentric support shaft disposed parallel to said platen, a hollow guide sleeve, and a carriage slidably supported by said hollow guide sleeve and supporting said print head, said eccentric support shaft consisting of an intermediate portion and opposite end portions at which said eccentric support shaft is rotatably supported by a frame of the printing apparatus, said intermediate and eccentric portions being eccentric with each other, and said hollow guide sleeve being disposed radially outwardly of and coaxially with said intermediate portion such that said hollow guide sleeve and said eccentric support shafts are rotatable relative to each other, said drive force of said drive source rotating said eccentric support shaft. 
     
     
       28. A method of adjusting a head gap in a printing apparatus, said apparatus comprising a platen for supporting a recording medium; a print head disposed movably in a transverse direction toward and away from said platen;   a head advancing and retracting device for moving said print head in said transverse direction;   automatic head gap adjusting means for controlling said head advancing and retracting device to advance said print head until the print head comes into contact with said recording medium and then retracting the print head by a predetermined distance to adjust a head gap between said recording medium and said print head;   said head advancing and retracting device comprising a drive source, a power transmission mechanism for transmitting a drive force of said drive source to said print head to move the print head in said transverse direction, and a clutch mechanism having a connecting state for transmitting said drive force of said drive force smaller than a preset value in a forward direction to advance the print head toward said platen, and a disconnecting state for inhibiting the transmission of said drive force exceeding said preset value to said print head; and   said automatic head gap adjusting means comprising clutch release detecting means for detecting said disconnecting state of said clutch mechanism, and stopping means for stopping an operation of said drive source that produces the drive force in said forward direction, when said disconnecting state of said clutch mechanism is detected by said clutch release detecting means, comprising the steps of:   positioning said print head at a predetermined position which is spaced from said platen by a known distance;   operating said automatic head gap adjusting means to advance said print head until the print head comes into contact with said platen, with no recording medium placed on said platen, and determining a first advancing distance of said print head between said predetermined position and a position at which the print head contacts said platen;   calculating a difference between said known distance and said first advancing distance, as a specific value inherent to the printing apparatus;   retracting said print head and placing the recording medium on said platen;   operating said automatic head gap adjusting means again to advance said print head, until the print head comes into contact with the recording medium placed on said platen; and   retracting said print head by a distance equal to a sum of said specific value and a nominal head gap value.   
     
     
       29. A method of adjusting a head gap in a printing apparatus having a platen for supporting a recording medium, (b) a print head disposed movably in a transverse direction toward and away from said platen, (c) a head advancing and retracting device for moving said print head in said transverse direction, and (d) automatic head gap adjusting means for controlling said head advancing and retracting device to advance said print head until the print head comes into contact with said recording medium and then retracting the print head by a suitable distance, to thereby adjust said head gap between said recording medium and said print head, said method comprising the steps of: positioning said print head at a predetermined position which is spaced from said platen by a known distance;   operating said automatic head gap adjusting means to advance said print head until the print head comes into contact with said platen, with no recording medium placed on said platen, and determining a first advancing distance of said print head between said predetermined position and a position at which the print head contacts said platen;   calculating a difference between said known distance and said first advancing distance, as a specific value inherent to the printing apparatus;   retracting said print head and placing the recording medium on said platen;   operating said automatic head gap adjusting means again to advance said print head, until the print head comes into contact with the recording medium placed on said platen; and   retracting said print head by a distance equal to a sum of said specific value and a nominal head gap value, said sum consisting of said suitable distance.   
     
     
       30. A printing apparatus comprising: a platen for supporting a recording medium;   a print head disposed movably in a transverse direction toward and away from said platen;   a head advancing and retracting device for moving said print head in said transverse direction;   said head advancing and retracting device comprising a drive source, a power transmission mechanism for transmitting a drive force of said drive source to said print head to move the print head in said transverse direction, and a clutch mechanism having a connecting state for transmitting said drive force of said drive source smaller than a preset value in a forward direction to advance the print head toward said platen, and a disconnecting state for inhibiting the transmission of said drive force exceeding said preset value to said print head; and   said clutch mechanism comprising a drive member, a driven member, a first and a second engaging portion which are provided on one and the other of said drive and driven members, respectively, and an elastic member, said first and second engaging portions engaging each other such that a movement to retract said print head is transmitted from said drive member to said driven member while a movement to advance the print head is inhibited from being transmitted from the drive member to the driven member, said elastic member having a predetermined pre-load biasing said first and second engaging portions of said drive and driven members for engagement of said first and second engaging portions with each other, said pre-load being smaller than said drive force of said drive member.   
     
     
       31. A printing apparatus according to claim 30 wherein said drive and drive members are rotating members, and one of said first and second engaging portions consists of a pin which is secured to said one of said drive and driven members so as to extend parallel to axes of rotation of said drive and driven members, while the other of said first and second engaging portions consists of a recess which is formed in said other of said drive and driven members so that said pin engages said recess with a play in a rotating direction of said other of the drive and driven members, said elastic member biasing said pin against one of opposite ends of said recess in said rotating direction.